So use multi-signature transactions right? Great!
Now ask yourself, why isn't multi-sig more prevalent? Because its usability is still awful.
It's still beyond the average user to set up, maintain, and spend from multi-sig addresses. Various online tools exist that can help, but running to a hosted website for each new spend or multi-sig address shouldn't be the end-all solution for bitcoin users. Instead, it should be possible to design a locally run wallet with a simple user interface that can easily split up the control over multiple devices.
I'm posting it here for comment and critique because I just want to know if this idea sounds feasible. Feel free to poke holes in it and call out what doesn't make sense. If executed properly, we'll end up with a dynamic program that can create a variety of customized, secure, and persistent multi-sig setups.
2-of-2 setup
2-of-3 setup.